Switch from `when` to `bluebird` for Promise implementation.

Bluebird is very fast.

Change-Id: I7e4718e7b0bd61a774fef1c9dfa7748cd4ab1fce
Switch from `bluebird` to `es6-shim`/`prfun` for Promise implementation.

Use standard ES6 promises.

Change-Id: I1c698ed05453f22b1574aa4e59eef7463f5cec59